Method of selective recovery of valuable metals from mixed metal oxides

ABSTRACT

The present invention relates to a process for recovering metals from indium tin oxide (ITO) scrap. It allows the selective recovery of indium and tin from waste ITO by means of a simple and environmentally benign dissolution-deposition method, with no requirement of using strong corrosive acid/alkaline chemicals (e.g. hydrochloric acid, nitric acid, sulfuric acid and sodium hydroxide) for dissolution and complicated procedures/operation. The dissolution baths can be reused without observable recovery deterioration. It significantly reduces the cost requirement in the recovery process.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority of U.S. provisional patentapplication Ser. No. 61/966,180 filed Feb. 18, 2014, and the disclosureof which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates a method of selective recovery of indiumand tin from ITO waste through sequential dissolution and deposition,involving the method and bath formulations to selectively dissolveindium and tin from ITO waste and how to collect indium and tin from thesolution.

BACKGROUND OF THE INVENTION

Indium is an important element in electronic and energy-relatedindustries. Its compound indium oxide (In₂O₃) plays an important role intransparent conductive oxide (TCO), which is an essential material forflat panel display, solar cell and other applications. Due to its risingdemand and difficulties in extraction, a shortage of indium and risingprices are expected in the future. The establishment of a safe andcost-effective method for recovering indium from indium-containing wasteis, therefore, of great importance.

There are many research groups working on ITO waste recovery and none ofthem uses the current invention to selectively recover indium and tinfrom the ITO waste. Park et al. (Silla University) reported a method torecover indium metal from ITO scrap with purity up to 99%. However, theprocess needed to use highly corrosive medium (i.e. 50% sodiumhydroxide) in an indium precipitation bath at 140° C. for 4 hours, whichare generally not recommended in large scale production purpose (Bull.Korean Chem. Soc., 2011, 32, 3796). Li et al. (Central South University)proposed a method to leach ITO from the waste using H₂SO₄ and HCl, andremove tin from the leach solution by sulphidation. However, hydrogensulfur (H₂S) gas was used as the sulphidation agent which is highlytoxic and combustible gas (Hydrometallurgy, 2011, 105, 207). Benedettoet al. (Cidade Universitaria) proposed the use of organic phosphoricacid-based extractants (e.g D2EHPA) to selective extract indium fromITO-containing leach solution. However, the materials cost of theseproprietary extractants is relatively high (Minerals Eng., 1998, 11,447). In the above reports, they all carried out their studies usingeither highly corrosive chemicals or proprietary extractants, and usedto produce a lot of waste in the processes.

Therefore, low-cost, less toxic and reusable formulations for recoveringindium and tin from ITO-containing waste are also need in the industry.

SUMMARY OF THE INVENTION

The present invention allows selective recovery of indium and tin fromITO waste through a simple and environmentally benign process, with norequirement of using corrosive acid and alkaline (e.g. hydrochloricacid, nitric acid, sulfuric acid and sodium hydroxide) and complicatedprocedures/operation. Hence, the present invention significantly reducesthe cost and energy requirement in the recovery process. As the presentmethod uses a greener recycling solution, it also reduces the impact onthe environment.

Accordingly, the first aspect of the present invention relates to adissolution-deposition process for selectively recovering indium and tinfrom ITO waste. To recover indium, the process of the present inventioncomprises the following steps:

a) reducing the size of ITO-containing materials by shredding andcrushing so as to form finely-divided particles;

b) subjecting the finely-divided particles to chemical and physicalcleaning for pre-treatment to substantially avoid the interference indissolution step;

c) transferring the pre-treated particles to a first dissolution bathcomprising a first bath formulation at a bath temperature ranging from60° C. to 120° C. with continuous stirring for 30-180 minutes todissolve the pre-treated particles;

d) adding 50-300% by volume of water into the solution containing thedissolved particles from step (c) to form a first mixture and filteringthe first mixture so as to collect an indium-rich filtrate and atin-rich filtrand;

e) putting an indium plate in the indium-rich filtrate for 1-10 hours toremove the tin residue by a displacement reaction;

f) recovering indium with purity not less than 99.9% from theindium-rich filtrate by a first deposition process;

g) reusing the dissolution bath in step (c) for the next recovery cycleafter water evaporation.

To recover tin, the process of the present invention further comprisesthe following steps:

h) transferring the tin-rich filtrand obtained from step (d) to a seconddissolution bath comprising a second bath formulation at a bathtemperature ranging from 60° C. to 120° C. with continuous stirring for30-180 minutes to dissolve the tin-rich filtrand;

i) adding 50-300% by volume of water into the solution containing thedissolved tin-rich filtrand to form a second mixture and filtering thesecond mixture so as to collect tin-rich filtrate and non-dissolvedsubstrates;

j) recovering tin from the tin-rich filtrate obtained in step (i) by asecond deposition process;

k) reusing the second dissolution bath in step (h) for the next recoverycycle after water evaporation.

The second aspect of the present invention relates to bath formulationsfor recovering indium and tin respectively following thedissolution-deposition process of the present invention. Both the firstand second bath formulations for dissolving indium and tin respectivelyare comprised of low-cost and less corrosive compounds, as opposed toconventional bath formulations which contain highly corrosive sodiumhydroxide, hydrochloric acid and sulfuric acid. In one embodiment, thefirst bath formulation used in the dissolution-deposition process of thepresent invention comprises a mixture of organic halide and dicarboxylicacid. In another embodiment, the second bath formulation used in thedissolution-deposition process of the present invention comprises amixture of organic halide and carboxylic acid.

As compared to conventional process of recovering indium and tin fromITO-containing materials, the whole process of the present invention isdone at relatively low temperature, which does not require large amountof energy. The ionic solvents in the bath formulations of the presentinvention can also be reused after simple water evaporation withoutobservable recovery deterioration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart depicting the dissolution-deposition process ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the presently preferredembodiment of the present invention, serve to explain the principles ofthe invention. These embodiments or examples are described in sufficientdetail to enable those skilled in the art to practice the invention, andit is to be understood that other embodiments may be utilized, and thatchanges may be made without departing from the spirit of the presentinvention.

Example 1 Composition of Bath Formulations For Indium/Tin Recovery

The first bath formulation for recovering indium from pre-treatedITO-containing particles mainly comprises the following two components:

a) One or more than one kind of organic halide salts: The cation ofthese organic halide salts can be but not limited to tetraalkylammonium,(di-, tri- and tetra alkyl)imidazolium, alkylpyridinium,dialkylpyrrolidinum, dialkylpiperidinium, tetraalkylphosphonium,tetralkylsulfonium, dialkylpyrazolium, and N-alkylthiazolium. In thisexample, 2-hydroxy-N,N,N-trimethylethanaminium chloride (cholinechloride) is used as the organic halide salts in the first bathformulation;

b) 20-80 mol % of dicarboxylic acid: The dicarboxylic acid can be butnot limited to oxalic acid, malonic acid, succinic acid, glutaric acid,and adipic acid. In one embodiment, the molar ratio between the organichalide salts and dicarboxylic acid in the first bath formulation isabout in 1:1.

The second bath formulation for recovering tin from a tin-rich material(e.g. the tin-rich filtrand obtained from the ITO-containing scrapaccording to the dissolution-deposition process of the presentinvention) comprises the following two components:

a) One or more than one kind of organic halide salts: The cation ofthese organic halide salts can be but not limited to tetraalkylammonium,(di-, tri- and tetra alkyl)imidazolium, alkylpyridinium,dialkylpyrrolidinum, dialkylpiperidinium, tetraalkylphosphonium,tetralkylsulfonium, dialkylpyrazolium, and N-alkylthiazolium. In thisexample, 2-hydroxy-N,N,N-trimethylethanaminium chloride (cholinechloride) is used as the organic halide salts in the second bathformulation;

b) 20-80 mol % of carboxylic acid: The carboxylic acid can be but notlimited to trifluoroacetic acid, trichloroacetic acid, dichloroaceticacid, chloroacetic acid, propanoic acid, butyric acid, and valeric acid.

In one embodiment, the molar ratio between the organic halide salts andcarboxylic acid in the second bath formulation is about in 1:2.

Example 2 Electrodeposition Conditions for Collecting Indium/Tin fromBath Formulations with Dissolved Indium and/or Tin

In Example 1, after dissolving the pre-treated particles ofITO-containing waste into the first bath formulation and being addedwith water by volume of 50-300%, the solution is filtered and theindium-rich filtrate is separated from the tin-rich filtrand. To collectindium from the indium-rich filtrate, an indium plate is put into thefiltrate to remove any residual tin in the filtrate followed by thefirst electrodeposition process under the following conditions: pH nothigher than 1.5; current density from 0.6 to 4 mA/cm² or voltage from 2Vto 4V, more preferably the voltage is at about 2.6V; electrodepositiontime: 30-90 minutes; temperature from 60° C. to 120° C. Indium metal isdeposited electrochemically on a substrate from the tin-rich filtrate inan electrochemical cell. The substrate can be but not limited totitanium, stainless steel and graphite. The counter electrode can be butnot limited to titanium, platinum and graphite.

The tin-rich filtrand obtained from filtration of the first mixture isthen dissolved in the second bath formulation before being added withwater by volume of 50-300% to form a second mixture. The second mixtureis filtered to obtain a tin-rich filtrate and a filtrand containingnon-dissolved substrates. The tin-rich filtrate is then subjected to thesecond electrodeposition process under the following conditions: pH nothigher than 1; current density from 0.8 to 5 mA/cm² or voltage from 2.2Vto 4.5V, more preferably the voltage is at about 3.2V; electrodepositiontime: 30-90 minutes; temperature from 60° C. to 120° C. Tin metal isdeposited electrochemically on a substrate from the tin-rich filtrate inan electrochemical cell. The substrate can be but not limited totitanium, stainless steel and graphite. The counter electrode can be butnot limited to titanium, platinum and graphite.

Example 3 Recovery of Indium and Tin from ITO-containing Scarp UsingBath Formulations and Electrodeposition Process of The Present Invention

In FIG. 1, the recovery route of indium and tin is composed of threemain steps. First, the collected and manufacturing ITO-containing scarpare crushed to reduce the waste size, and chemically washed to eliminatethose organic residues (e.g. liquid crystals (LCs) in liquid crystaldisplays (LCDs)). Afterwards, the pre-treated powder is transferred intothe dissolution bath containing the respective ionic solvent, such asthe first bath formulation for dissolving indium in Example 1. In afirst dissolution bath, indium and tin are dissolved from ITO (Eqn. 1and 2), and stabilized as In(X)₂ ⁻ and Sn(X)₂ respectively (Eqn. 3 and4).

In₂O₃+6H⁺=2In³⁺+3H₂O  (Eqn. 1)

SnO₂+4H⁺=Sn⁴⁺+2H₂O  (Eqn. 2)

In³⁺+2X ²⁻=In(X)₂ ⁻  (Eqn. 3)

Sn⁴⁺+2X ²⁻=Sn(X)₂  (Eqn. 4)

X: dicarboxylic acid

As the ionic solvent in the first dissolution bath exhibits dissolutionselectivity for In(X)₂ ⁻ and precipitation ability for Sn(X)₂, tin-richfiltrand can be separated from the mixture through filtration by anysuitable filtering means, e.g., glass microfiber and membrane filter.Indium metal can then be collected from the bath through theelectrodeposition process under certain conditions such as therespective conditions for indium recovery in Example 2.

As it is evident from inductively coupled plasma atomic emissionspectroscopy (ICP-OES) (Table 1), contents of indium and tin in raw ITOscrap is about 85:15 ratio. By mixing with the first bath formulation inExample 1, for example, a mixture of2-hydroxy-N,N,N-trimethylethanaminium chloride (organic halide salt)with oxalic acid (dicarboxylic acid) in 1:1 molar ratio, it exhibitsdissolution selectivity for indium over tin. In the dissolution process,indium is well-dissolved in the reaction medium and most tin oxides areprecipitated. After filtration, the indium to tin ratio in the filtrateincreases up to 96:4. If the molar ratio of2-hydroxy-N,N,N-trimethylethanaminium chloride and oxalic acid ischanged to 2:1 or 1:2, there is no significant change in the indium totin ratio in the resulting filtrand; however, it takes highertemperature (about 120° C.) and longer time (about 180 minutes) tocomplete the dissolution process. By replacing the dicarboxylic acidwith carboxylic acid (e.g. trichloroacetic acid) in the second bathformulation as in Example 1, both indium and tin are well-dissolved inthe reaction medium. It exhibits no dissolution selectivity and hencecontents of indium and tin after dissolution process is still about85:15 ratio.

TABLE 1 ICP samples In:Sn ratio Purity, % Raw ITO scrap  85:15 85% Afterdissolution process 96:4 96% After displacement reaction 99.95:0.0599.95%  

To further reduce the tin content in the filtrate, a galvanicdisplacement process by indium plate is used to remove the tin impurity.In comparison, indium metal is more reductive. It can take the place oftin in the ionic solvents and promote tin deposition. After thedisplacement reaction, indium metal is electrochemically deposited on asubstrate (e.g. titanium, stainless steel and graphite) and the indiumpurity can further increase to >99.9%.

To recover metal tin from the tin-rich filtrand, the tin-rich filtrandis re-dissolved into a second dissolution bath comprising a second bathformulation, such as the second bath formulation in Example 1 fordissolving tin. As the second bath formulation for tin recovery showsgood solubility for the tin precipitate, the residues (e.g. glass andplastic) can be easily separated from the mixture by any suitablefiltering means, e.g. glass microfiber filter and membrane filter. Tinmetal can then be collected from the bath through the electrodepositionprocess under certain conditions such as the respective conditions fortin recovery in Example 2.

Since the chemical composition of the bath formulations after each ofthe dissolution steps is basically unchanged, they can be reused withoutobservable recovery deterioration but simply evaporating the excesswater.

INDUSTRIAL APPLICABILITY

The presently claimed method and formulations for dissolving andrecovering indium and tin respectively from ITO-containing waste areuseful in both waste management and treatment plant for ITO-containingwaste such as display panel. The present formulations for dissolvingindium and tin comprised of less corrosive and less toxic substancesthan the conventional formulations are reusable without observablerecovery deterioration while the composition of the formulations aresubstantially unchanged after water evaporation, thereby becoming abetter alternative to the conventional formulations in terms of cost andpollution to our environment.

It is understood that the method/device/system described herein may beperformed in different order, concurrently and/or together with othersteps not mentioned herein but readily appreciated by one skilled in theart to obtain the method/device/system of the present invention. Withoutfurther elaboration, it is believed that one skilled in the art can,based on the description herein, modify the present invention withoutdeparting the spirit of the present invention and utilize the presentinvention to its fullest extend. All publication recited herein arehereby incorporated by reference in their entirety.

What is claimed is:
 1. A method for sequentially recovering indium andtin from ITO-containing waste comprising: a) reducing the size ofITO-containing materials by shredding and crushing so as to formfinely-divided particles; b) subjecting the finely-divided particles tochemical and physical cleaning for pre-treatment to substantially avoidthe interference in dissolution step; c) transferring the pre-treatedparticles to a first dissolution bath comprising a first bathformulation at a bath temperature ranging from 60° C. to 120° C. withcontinuous stirring for 30-180 minutes to dissolve the pre-treatedparticles; d) adding 50-300% by volume of water into the solutioncontaining the dissolved particles from step (c) to form a first mixtureand filtering the first mixture so as to collect an indium-rich filtrateand a tin-rich filtrand; e) putting an indium plate in the indium-richfiltrate for 1-10 hours to remove the tin residue by a displacementreaction; f) recovering indium with purity not less than 99.9% from theindium-rich filtrate by a first deposition process; g) reusing thedissolution bath in step (c) for the next recovery cycle after waterevaporation.
 2. The method of claim 1, further comprising: h)transferring the tin-rich filtrand obtained from step (d) to a seconddissolution bath comprising a second bath formulation at a bathtemperature ranging from 60° C. to 120° C. with continuous stirring for30-180 minutes to dissolve the tin-rich filtrand; i) adding 50-300% byvolume of water into the solution containing the dissolved tin-richfiltrand to form a second mixture and filtering the second mixture so asto collect tin-rich filtrate and non-dissolved substrates; j) recoveringtin from the tin-rich filtrate obtained in step (i) by a seconddeposition process; k) reusing the second dissolution bath in step (h)for the next recovery cycle after water evaporation.
 3. The method ofclaim 1, wherein the first bath formulation comprises the followingcomponents: one or more than one kind of organic halide salts, whereincation of the organic halide salts comprise tetraalkylammonium, (di-,tri- and tetra alkyl)imidazolium, alkylpyridinium, dialkylpyrrolidinum,dialkylpiperidinium, tetraalkylphosphonium, tetralkylsulfonium,dialkylpyrazolium, and N-alkylthiazolium; and 20-80 mol % ofdicarboxylic acid, said dicarboxylic acid comprising oxalic acid,malonic acid, succinic acid, glutaric acid, and adipic acid.
 4. Themethod of claim 3, wherein the cation of the organic halide salts istetraalkylammonium and the dicarboxylic acid is oxalic acid; saidorganic halide salts and dicarboxylic acids are in a molar ratio of 1:1.5. The method of claim 1, wherein the first deposition process is anelectrodepsition process of indium comprising the following operationconditions and/or components: a pH of not higher than 1.5; currentdensity from 0.6 to 4 mA/cm² or voltage from 2V to 4V; electrodepositiontime from 10 to 60 minutes; temperature from 20° C. to 70° C.; asubstrate for electrodepositing indium from the indium-rich filtratecomprising titanium, stainless steel and graphite; and a counterelectrode comprising titanium, platinum and graphite.
 6. The method ofclaim 2, wherein the second bath formulation comprises the followingcomponents: one or more than one kind of organic halide salts, whereincation of the organic halide salts comprise tetraalkylammonium, (di-,tri- and tetra alkyl)imidazolium, alkylpyridinium, dialkylpyrrolidinum,dialkylpiperidinium, tetraalkylphosphonium, tetralkylsulfonium,dialkylpyrazolium, and N-alkylthiazolium; and 20-80 mol % of carboxylicacid, said carboxylic acid comprising trifluoroacetic acid,trichloroacetic acid, dichloroacetic acid, chloroacetic acid, propanoicacid, butyric acid, and valeric acid.
 7. The method of claim 6, whereinthe cation of the organic halide salts is tetraalkylammonium and thecarboxylic acid is trichloroacetic acid; said organic halide salts andcarboxylic acids are in a molar ratio of 1:2.
 8. The method of claim 2,wherein the second deposition process is an electrodeposition process oftin comprising the following operation conditions and/or components: apH of not higher than 1; current density from 0.8 to 5 mA/cm² or voltagefrom 2.2V to 4.5V; electrodeposition time from 10 to 60 minutes;temperature from 20° C. to 70° C.; a substrate for electrodepositing tinfrom the tin-rich filtrate comprising titanium, stainless steel andgraphite; and a counter electrode comprising titanium, platinum andgraphite.
 9. The method of claim 1, wherein the displacement reactioncomprises a galvanic displacement process by an indium plate forremoving tin residues from the indium-rich filtrate after said firstdeposition process.
 10. The method of claim 1, wherein theITO-containing materials comprises ITO-containing scraps andITO-containing powders from display panel, solar cell panel, or consumerelectronic by-products.
 11. A bath formulation for dissolving indium toform an indium-rich solution, said formulation comprising: one or morethan one kind of organic halide salts, wherein cation of the organichalide salts comprise tetraalkylammonium, (di-, tri- and tetraalkyl)imidazolium, alkylpyridinium, dialkylpyrrolidinum,dialkylpiperidinium, tetraalkylphosphonium, tetralkylsulfonium,dialkylpyrazolium, and N-alkylthiazolium; and 20-80 mol % ofdicarboxylic acid, said dicarboxylic acid comprising oxalic acid,malonic acid, succinic acid, glutaric acid, and adipic acid.
 12. Thebath formulation of claim 11, wherein the cation of the organic halidesalts is tetraalkylammonium and the dicarboxylic acid is oxalic acid;said organic halide salts and dicarboxylic acids are in a molar ratio of1:1.
 13. A bath formulation for dissolving tin to form a tin-richsolution, said formulation comprising: one or more than one kind oforganic halide salts, wherein cation of the organic halide saltscomprise tetraalkylammonium, (di-, tri- and tetra alkyl)imidazolium,alkylpyridinium, dialkylpyrrolidinum, dialkylpiperidinium,tetraalkylphosphonium, tetralkylsulfonium, dialkylpyrazolium, andN-alkylthiazolium; and 20-80 mol % of carboxylic acid, said carboxylicacid comprising trifluoroacetic acid, trichloroacetic acid,dichloroacetic acid, chloroacetic acid, propanoic acid, butyric acid,and valeric acid.
 14. The bath formulation of claim 13, wherein thecation of the organic halide salts is tetraalkylammonium and thecarboxylic acid is trichloroacetic acid; said organic halide salts andcarboxylic acids are in a molar ratio of 1:2.